Conventionally, a plurality of electronic devices, called in-vehicle ECUs, are installed in a vehicle, and operate in a coordinated manner while exchanging information with each other via a network such as a CAN (Controller Area Network), thereby realizing control relating to, for example, running of the vehicle and comfort in the vehicle interior and the like. Furthermore, the in-vehicle ECUs are connected to an electric power supply, such as a battery or an alternator, of the vehicle via electric power lines, and operate with electric power supplied from the electric power supply. In recent years, the number of in-vehicle ECUs installed in a vehicle has increased, leading to a demand for power saving.
Furthermore, with high functionality of a vehicle, a plurality of sophisticated microcomputers (hereinafter, referred to simply as “microcomputers”) are installed for in-vehicle ECUs. In order to drive these microcomputers, the electric power consumption and dark currents increase, which may cause a battery to run out and fuel efficiency to deteriorate. Accordingly, it is a common practice that a microcomputer has a HALT mode (mode in which instruction execution of a CPU is interrupted) and a STOP mode (mode in which operations of the CPU and peripheral circuits are stopped), and operates intermittently in a normal mode, with the above-described HALT mode (STOP mode) inserted therein.
A drive control apparatus for an in-vehicle device that is disclosed in Patent Document 1 is taken as an example of an in-vehicle ECU that can reduce electric power consumption. This control apparatus includes an approach sensor for detecting an object that approaches a vehicle, and a controller intermittently switches the approach sensor on to drive it intermittently. If the approach sensor, when intermittently driven by the controller, detects an object approaching the vehicle, the controller starts driving an intrusion sensor that is subjected to drive control and remains undriven until then.